Floods in Saint-Petersburg
As most of the cities situated on a large rivers or in deltas, Saint-Petersburg was always in danger of flooding. However, unlike the most places, the reason for the rise of the water is not the inflow from the river (Neva-river), but rather of back flow of the water from the sea, cased by strong westerly winds forming a Kelvin wave causing a Storm surge. Storm surge happens when strong winds blowing in constant direction push the water mass in that direction increasing the water level. A combination of specific features observed at Neva-river delta area intensifies the effect of the storm surge:
1. Persistent westerly winds in fall-winter lasting for several days
2. Saint-Petersburg is located at the tip of gradually narrowing Finnish Gulf. As the surge wave progresses into narrowing space the height of it increases.
3. The Finish Gulf is pretty shallow with flat bottom. The effect of the storm surge is higher in the shallow environment, compared to deep environment.
The state of flood is declared when the water rises more than 160 cm from its standard level. The classification of floods by the water level rise is as follows:
- 160 - 210 cm: Dangerous flood
- 210 - 300 cm: Very dangerous flood
- more than 300 cm: Catastrofic flood
Up to February of 2002 there were registered 228 dangerous floods, 66 very dangerous, and 3 catastrophic.
Since the city was founded in 1703, the highest registered water level was more than 4 m. But the highest level of all occurred in 1691, according to Swedish chronicles the water level reached 7.5 m height.
In the past high floods were disastrous for the city with several hundreds deaths and destruction of wooden houses in the low laying areas. As the flooding period is September-December, the situation would be worsened by the freezing cold water temperatures and, obviously, strong winds.
You can understand how catastrophic could be the floods by standing near the obelisk and imagining the water level being at the highest mark. The important thing to know during this exercise is that the natural river shore, as in all river deltas, is very low. The high embankment is artificial.
To claim this cache you need:
In your log report the water level observed at the time of your visit.
Also send me a message with the answers on the following questions:
1: There are several iron bands on the obelisk marking few highest levels of water. Report the year and the height for each band. (there are more than two bands, to see them all you have to look over the railings or go down to the water by the granite stairs)
2: How high the measuring scale goes on the obelisk?
3: What has been done to protect the city from the floods?
To answer questions 1 and 2 you need to collect information at the cache site. For question 3 use the Internet.
Posting a picture of yourself or your GPS with the obelisk on the background is optional.
You do not need to wait for the confirmation from me to log this Earthcache as a find. However, logs that do not fulfill the requirements will be deleted.
Important! Please be careful not to post pictures or specific information that can help others to answer the required questions without actually visiting the site. I will have to remove such logs.
